Phospholipids (PL) are known to possess various physiological functions, including brain function improving effect, anti-stress effect, and cholesterol reducing action. PL occur in various forms, well-known examples of which include phosphatidylcholine (PC), phosphatidylserine (PS), phosphatidylethanolamine (PE), and phosphatidylinositol (PI). These different forms of PL have different functions and properties.
Among these different types of PL, phospholipids whose constituents are long-chain polyunsaturated fatty acids (may be referred to as “LCPUFA” hereinafter) with 20 or greater carbon atoms (may be referred to as “LCPUFA-PL” for convenience of explanation) are known to exhibit superior brain function improving effect, as compared with phospholipids whose constituents are not LCPUFA (may be referred to as “non-LCPUFA-PL” for convenience of explanation) (see Non-Patent Publication 1, for example). Specific examples of LCPUFA include, for example, docosahexaenoic acid (DHA), arachidonic acid (AA) and the like.
Non-phospholipid LCPUFA derivatives are also known to possess brain function improving effects (see Patent Publication 1, for example). However, unlike phospholipids such as the LCPUFA-PL or Non-LCPUFA-PL, the non-phospholipid LCPUFA derivatives are believed to act on the hippocampus of the cerebrum to improve the brain functions.
The LCPUFA-PL is considered to provide superior brain function improving effect because (1) it has the structure actually present in the brain, (2) it can pass through the blood brain barrier, and (3) it can reach the brain tissue or other tissues in the body without being captured or modified in the liver, since the molecule is absorbed without entering the liver.
The following more specifically describes these reasons. (1) The LCPUFA in the brain is known to exist almost entirely in the form of phospholipids. More specifically, most of LCPUFA exist as compounds such as PC, PS, PE, and PI, and therefore exhibit a variety of functions in the brain. (2) The phospholipids can reach the brain tissue. This has been proved by an experiment in which orally administered labeled-phospholipids were detected in the brain tissue (see Non-Patent Publication 2). (3) When absorbed, one of the two fatty acid molecules of the phospholipids is hydrolyzed to generate lysophospholipids in the digestive system. The lysophospholipids are absorbed in the small intestine and reassembled into phospholipids in the small intestine cells before they are absorbed through the lymph vessels (Non-Patent Publication 3). In this manner, the LCPUFA-PL circulates through the body without entering the liver.
Conventionally, the LCPUFA-PL has been produced by being prepared or purified from organs, eggs, or other parts of animals containing a large amount of LCPUFC-PL. In one specific example, the LCPUFA-PL is prepared from the cow brain, or a phospholipid fraction from the pig liver or fish egg is purified (see Patent Publications 2 and 3). Further, particular species of marine bacteria are known to produce LCPUFA-PL (see Non-Patent Publication 4). Furthermore, it is also known that arachidonic acid-producing filamentous bacteria produce a small amount of phospholipids containing arachidonic acid in addition to a large amount of triglycerides containing arachidonic acid (see Non-Patent Publication 5).
In the industrial production of phospholipids, phospholipids are generally extracted together with oil or fat, when the oil or fat, of which primary ingredient are triglycerides, is extracted from a starting material. Hexane or the like solvent is used as a solvent for extraction.
The extracted oil or fat includes gum substance, which may cause the coloring and foaming of the oil or fat. Therefore the gum substance is removed through a gum-removing process, in which almost all parts of phospholipids are transferred to the gum substance. Accordingly, phospholipids are produced by purification of the gum substance.
In the case where soy bean lecithin is produced as phospholipids, raw oil is extracted from soy, which is a starting material in this case, by using hexane as a solvent. The residual defatted soy is used as food, feedstuff or the like. As the raw oil, on the other hand, includes gum substance, the gum substance is separated through a gum-removing process and then purified. Through the process the soy bean lecithin is produced. When the content of the soy bean lecithin or phospholipids is detected after the aforementioned series of production steps of the soy bean lecithin, from 1.5% to 2.5% of phospholipids is contained in the raw oil indeed, but the content of phospholipids in the purified oil is no more than 0.05%. Consequently, it becomes apparent that the phospholipids are removed mainly through gum-removing process (see Non-Patent Publication 6).
[Patent Publication 1]    Japanese Laid-Open Patent Publication No. 48831/2003 (Tokukai 2003-48831) (published on Feb. 21, 2003)
[Patent Publication 2]    Japanese Laid-Open Patent Publication No. 35587/1999 (Tokukaihei 11-35587) (Published on Feb. 9, 1999)
[Patent Publication 3]    Japanese Laid-Open Patent Publication No. 59678/1996 (Tokukaihei 08-59678) (Published on Mar. 5, 1996)
[Non-Patent Publication 1]    G. Toffano et al., Nature Vol. 260 p 331-333 (1976)
[Non-Patent Publication 2]    G. Toffano et al. Clinical Trial Journal Vol. 24 p 18-24 (1987)
[Non-Patent Publication 3]    Katsumi Imaizumi, Clinical Nutrition (Rinsho Eiyo), Vol. 67, p. 119 (1985)
[Non-Patent Publication 4]    Kazunaga Yazawa et al., Oil Science (Abura Kagaku), Vol. 44, pp. 787-793 (1995)
[Non-Patent Publication 5]    S. jareonkitmongkol et al., Apple Environ Microbiol Vol. 59 p 4300-4304 (1993)
[Non-Patent Publication 6]    Oils and Fats Handbook, Saiwai Shobou, p. 178-184 (1988)
But through the conventional techniques, it is difficult to produce LCPUFA-PL efficiently and stably.
Specifically, sources of LCPUFA-PL are limited and only a small amount of LCPUFA-PL can be obtained because the LCPUFA-PL currently available all derive from the aforementioned animal organs, or the egg yolk of animals. The supply is therefore unstable, and the same quality cannot always be obtained. Further, with the epidemic of the mad-cow disease, it has become very difficult to use the cow brain or other animal organs.
As for the technique using microbe, in the LCPUFA-PL derived from marine bacteria, the majority of its fatty acids are branched fatty acids which are distinct to bacteria and are rarely seen in humans or other animals. The LCPUFC-PL derived from marine bacteria is therefore not suitable as a nutritional composition for human consumption. Further, though arachidonic acid-producing filamentous bacteria produce phospholipids containing arachidonic acid, only a small amount is detected in a mixture of a large amount of triglycerides. Therefore it is difficult to apply this method in an industrial application.
The present invention was made in view of the foregoing problems. An object of the invention is to provide a technique to produce LCPUFA-PL efficiently and stably, and to provide low-cost LCPUFA-PL with a stable quality in stable quantity. Another object of the invention is to provide representative application of the technique.